Emerging evidences studying different types of cancer have revealed a relatively rare population of so called ''cancer stem cells'' (CSCs), also known as tumor-initiating cells (TICs), which share certain characteristics with normal stem cells, including a stem cell-like phenotype and function. However, little is known about the signaling networks that control and regulate the function of the TICs, particularly those that influence their cell growth properties in a normal or an inflammatory microenvironment. Also, intratumoral nutrient stress has been found even in early-stage cancers, and is correlated with poor patient survival. Therefore, understanding the signaling mechanisms governing cancer stem cell proliferation under inflammation and nutrient stress is of paramount importance for the identification of new and more selective therapeutic targets in cancer. In this proposal we will investigate the signaling and metabolic pathways that regulate the growth properties of TICs in vitro and in a relevant in vivo mouse cancer model. Signaling molecules that promote the survival of TICs will be promising tumor suppressor candidates. This project will investigate the metabolism reprogramming of TICs in the framework of a novel signaling pathway controlled by PKC?. Our preliminary results show that PKC? represses cell growth of human colorectal cancer cells under nutrient stress conditions, and that it plays a tumor suppressive role in a mouse model of intestinal carcinogenesis driven by APC mutation. Also the loss o of PKC? results in increased stem cell activity in the intestine in vivo and in organoids. Furthermore, PKC? is absent, or underexpressed, in several types of human cancers, including colorectal neoplasias. This is significant because colorectal cancer is one of the most prevalent neoplasias, affecting a large portion of the US population. Therefore, understanding how TICs are regulated by PKC? will be of relevant for a better understanding of tumor initiation and the identification of potentially novel therapeutic targets. Therefore, we will: (1) Characterize the rle of PKC? in cancer stem cell expansion and the effect of PKC?-controlled inflammatory signals in the tumor microenvironment; and (2) Determine the role of PKC? in cancer stem cell proliferative signaling focusing in the control of cancer cell metabolism. In summary, here we will rigorously test the hypothesis that PKC? ablation in the intestinal stem cells would account for the initiation factors increasing the number and proliferative activity of TICs. Therefore, a bette understanding of the signaling cascades that regulate cancer stem cell signaling would be of great impact as it will aid in the design of new more efficacious and selective therapies.